1. Field of the Invention
The present invention relates to an optical disc driving system and a method for determining the rotation speed of an optical disc, which are capable of optimally determining the rotation speed of the optical disc in accordance with environmental conditions.
2. Description of the Related Art
At present, such an optical disc, as CD, DVD or the like, is widely used as a recording medium for audio data and/or video data, and the requirements on the high-speed reading of the data in the optical disc are steadily increased. In conjunction therewith, the rotation speed of a disc spindle motor used for rotating the optical disc in an optical disc playback system is also increased.
Such an optical disc playback system is equipped with an optical pickup for reading out data recorded in the optical disc, a disc spindle motor for rotating the optical disc, a memory for temporarily storing the data thus read out, input/output means for supplying the data stored in the memory from the optical disc playback system to an external appliance and for receiving the data from the external appliance, and a control unit for controlling active elements in the optical disc playback system.
Moreover, the optical disc playback system is conventionally designed such that the disc spindle motor can be rotated at one of six different rotation speeds, such as the normal or rated rotation speed, two times, four times, eight times, twenty times and forty times as large as the normal rotation speed (hereinafter, they are represented as 2× speed, 4× speed, 8× speed, 20× speed and 40× speed, respectively). In the optical disc playback system, data recorded in the optical disc are initially read out at the highest rotation speed of the disc spindle motor. When failed in reading out the data at the highest rotation speed, the data in the disc is read out at a further reduced rotation speed of the disc spindle motor.
When succeeded in reading out the data at the reduced rotation speed, the rotation speed in this case is regarded as the rotation speed of reading-out in the optical disc playback system. However, when again failed in reading out the data at the reduced rotation speed, the rotation speed for the disc spindle motor has to be further reduced. When the data cannot be read out at the normal rotation speed even after the sequence of such processes, the optical disc playback system recognizes the failure in reading out the data of the optical disc at the normal rotation speed, and then the control unit informs the failure in reading out the data to a user via a display. Then, the optical disc playback system finishes the reading out of the data (see, for example, Japanese Unexamined Patent Application Publication No. 2001-291309).
However, an increased rotation speed of the disc spindle motor in the conventional optical disc driving system causes to increase the power consumption as well as to increase the intensity of noise. In a quiet environment as at midnight or early in the morning, the noise is particularly sticking out. Generally, the noise is a high frequency sound emanating from rotary elements, which rotate at a high speed, and therefore it is offensive to the ear.
When, moreover, the optical disc is rotated at high speed for long period, mechanical elements, such as the disc spindle motor, rotary shafts, and bearings therefore, suffer heavy load. When the disc spindle motor is driven under a heavy load condition, a greater amount of heat is generated from the disc spindle motor. Accordingly, it is necessary to install a cooling apparatus, such as an air-cooling fan or the like in the vicinity thereof.
In the case where the optical disc is rotated at high speed, several troubles may occur due to the inclusion of micro particles, such as dust, trash or the others, into spaces between frictional mechanical elements, such as bearings or the like, and therefore a very high precision is required to mount rotary elements onto the positions.